The present invention relates to methods for preparing tetrakis(pentafluorophenyl) borate salts used in conjunction with metallocene catalysts for olefin polymerization. More specifically, the present invention relates to novel methods for making trityl tetrakis(pentafluorophenyl) borate that is substantially free of ether and other oxygenated contaminants, and the tetrakis(pentafluorophenyl) borate salts used in its preparation.
Boron co-catalysts and their metallocene catalyst counterparts are highly effective in the polymerization of ethylene and propylene. Both components of such catalyst systems need to be free of contaminants that would interfere with the polymerization process since they are used at very low levels, compared to the weight of the monomer used in the reaction. Such contaminants include Lewis bases (substances that donate a pair of electrons). Therefore, safe and reliable processes for the manufacture of high purity trityl tetrakis(pentafluorophenyl) borate are desirable. More preferred are manufacturing processes for trityl tetrakis(pentafluorophenyl) borate that provide a product having consistent color and high purity. It has been determined that, with respect to purity, it is most desirable for trityl tetrakis(pentafluorophenyl) borates to be substantially free of ether (less than 0.5 wt %) and other oxygenated contaminants such as water.
There are few known methods for making trityl tetrakis(pentafluorophenyl) borate. One method, as described in U.S. Pat. No. 5,399,781, involves reacting lithium tetrakis(pentafluorophenyl) borate with trityl chloride in an alkane. This process yields, at least in part, trityl tetrakis(pentafluorophenyl) borate. Further, such processes described in the U.S. Pat. No. 5,399,781 patent can be achieved in the absence of ether solvents. In addition, the process for making the required starting material lithium tetrakis(pentafluorophenyl) borate can also be achieved in the absence of ether solvents. However, pentafluorophenyl lithium, from which lithium tetrakis(pentafluorophenyl) borate is made, is hazardous and must therefore be handled at low temperatures. This significantly complicates the process, ultimately affecting process costs. Thus, while suitable for small-scale laboratory operations, the above-described lithium tetrakis synthesis is not desirable for large-scale manufacture.
Sodium and potassium tetrakis(pentafluorophenyl) borates are known. The use of these materials for the preparation of trityl tetrakis(pentafluorophenyl) borate is suggested in EP 0 913 400 A1, although no experimental data was provided specifically for the preparation of the trityl borate. One method of preparing the potassium salt is known (A. G. Massey and A. J. Park, J. Organometallic Chem., 2 (1964) 245), but again, this method utilizes the lithium salt. Therefore, for the reasons already explained above, this method offers no better solution to the problem.
Mitsui et al. (EP 0 913 400 A1, 1999) describe the conversion of (C6F5)4BMgBr into the corresponding sodium salt. The bromomagnesium salt can be made more safely by using the Grignard reagent, C6F5MgBr. However, the conversion of the magnesium salt to the corresponding alkali metal borates involves treating the magnesium salt (in ether-toluene) with an aqueous solution of a sodium carboxylate, and extracting the aqueous layer with ethyl acetate. Although the purity of the desired sodium salt was acceptable according to fluorine NMR analysis, no indication was given as to the presence of residual solvents in the product.
In addition to the hazards associated with the use of pentafluorophenyl lithium, the crude mixture of LiCl and trityl tetrakis(pentafluorophenyl) borate was described in the prior art as a yellow solid. However, after removing the LiCl, the supposedly xe2x80x9cpurifiedxe2x80x9d product was not yellow, but was orange in color (an observation also made by Chien et al. who used the same process (J. Am. Chem. Soc., 113 (1991) 8570)). The change in color from yellow to orange in these prior art preparations of trityl tetrakis(pentafluorophenyl) borate is taken as an indication of the presence of the residual polar materials in the final product.
Prior art preparations of solid trityl tetrakis(pentafluorophenyl) borate have been isolated by removing methylene chloride solvent from the borate solution. If the removal of the last amount of the methylene chloride is vacuum assisted, the product tends to xe2x80x9cbloomxe2x80x9d or foam up, filling the entire vessel. Once the solvent is removed, the foamed trityl product is difficult to remove from the reaction vessel. This foaming inhibits the use of this process on a large scale.
As shown below in the Comparative Example section, when sodium tetrakis(pentafluorophenyl) borate is made according to EP 0 913 400 A1, ethyl acetate is clearly present as evidenced by proton NMR analysis. This illustrates the difficulty of removing coordinating contaminants from tetrakis(pentafluorophenyl) borate salts. In fact, this European patent discloses many ether complexes of borate salts, again indicative of the strong bond between the borate salts and ethers.
Thus, a safe, repeatable, and scaleable method for preparing trityl tetrakis(pentafluorophenyl) borate of consistent color and purity, while being essentially free of ether and other oxygen contaminants, is not known.
In accordance with one embodiment, the present invention relates to producing sodium or potassium tetrakis(pentafluorophenyl) borate that is substantially free of ether and other organic contaminants containing oxygen atoms. In a second embodiment, the invention relates to a method for producing trityl tetrakis(pentafluorophenyl) borate from the corresponding alkali metal salt.
More specifically, the present invention relates to a method for making lithium, sodium or potassium tetrakis(pentafluorophenyl) borate that is substantially free of ether and other organic contaminants containing oxygen atoms from a pentafluorophenyl magnesium bromide compound. Preferably, the (pentafluorophenyl) magnesium bromide is reacted in an ether solvent with a tris(pentafluorophenyl) borane in an aromatic hydrocarbon solvent to produce tetrakis(pentafluorophenyl) borate magnesium bromide. The tetrakis(pentafluorophenyl) borate magnesium bromide is then reacted with an aqueous solution of a halide selected from the group consisting of sodium chloride and potassium chloride to create an organic phase containing a product compound selected from the group consisting of tetrakis(pentafluorophenyl) borate sodium salt and tetrakis(pentafluorophenyl) borate potassium salt. The organic phase is separated, and the solvent is removed from the organic phase to provide a substantially ether-free compound selected from the group consisting of sodium tetrakis(pentafluorophenyl) borate and potassium tetrakis(pentafluorophenyl) borate. Most preferably, the product compound comprises less than about 0.5 weight percent ether.
In accordance with a further embodiment, the present invention relates to the manufacture of trityl tetrakis(pentafluorophenyl) borate by first providing a substantially ether-free compound selected from the group consisting of sodium tetrakis(pentafluorophenyl) borate and potassium tetrakis(pentafluorophenyl) borate. The substantially ether-free compound is then reacted with a trityl halide in a hydrocarbon liquid to form a slurry of trityl tetrakis(pentafluorophenyl) borate and a halide in a hydrocarbon liquid. The trityl tetrakis(pentafluorophenyl) borate and halide is then separated from the hydrocarbon liquid by a suitable method, such as filtration or decantation, followed by dissolving the trityl tetrakis(pentafluorophenyl) borate in a halogenated solvent to form a solution, said solvent not containing oxygen, nitrogen or other coordinating atoms. The trityl tetrakis(pentafluorophenyl) borate solution is then diluted in a hydrocarbon solvent having a higher boiling point than the halogenated solvent. Finally, the halogenated solvent and the hydrocarbon solvent are removed to provide pure trityl tetrakis(pentafluorophenyl) borate product. Most preferably, the product compound comprises less than about 0.1 weight percent ether.
In a more preferred embodiment, the present invention relates to manufacturing compounds having the formula (C6F5)4BM, wherein M=Na or K, by first reacting pentafluorophenyl magnesium bromide in ether with tris(pentafluorophenyl) borane in an aromatic hydrocarbon (e.g. toluene, xylene, or ethylbenzene, and preferably toluene) at a temperature from about 20 to about 65xc2x0 C. to produce tetrakis(pentafluorophenyl) borate magnesium bromide. The mixture of tetrakis(pentafluorophenyl) borate magnesium bromide and solvent is reacted with an aqueous solution of sodium chloride or potassium chloride. During this step of the process, the (MgBr)+ cation in the borate salt is exchanged for Na+ or K+. The amount of NaCl or KCl used should be at least one mole per mole of tetrakis(pentafluorophenyl) borate magnesium bromide. Preferably, it is more than this so as to ensure a high degree of the desired exchange. Thus, an amount of from about 1 to about 20 molar equivalents may be used, and more preferably, from about 5 to about 10 molar equivalents. Sodium and potassium tetrakis(pentafluorophenyl) borate have good solubility in ether-toluene mixtures. The magnesium salts (e.g., MgBrCl) dissolve in the aqueous layer. This reaction is fairly rapid at room temperature and is complete in from about 15 to about 60 minutes with stirring. The two resultant phases are distinct and easily separated.
The organic phase which contains sodium tetrakis(pentafluorophenyl) borate or potassium tetrakis(pentafluorophenyl) borate is separated from the aqueous phase. Solvent is then removed in such a way as to provide substantially ether-free sodium tetrakis(pentafluorophenyl) borate or potassium tetrakis(pentafluorophenyl) borate. It is understood that the term xe2x80x9csubstantially ether-freexe2x80x9d refers to an ether content in the salt of less than about 5.0 weight percent, preferably less than about 3.0 weight percent, and more preferably less than about 1.0 weight percent. In order to achieve this, ether is removed by atmospheric distillation. The head temperature during the distillation must be as close to the boiling point of the aromatic hydrocarbon as possible at atmospheric pressure before the ether distillation is considered complete. For example, when toluene is the aromatic hydrocarbon, the further the head temperature is from the normal boiling point for toluene of 110xc2x0 C., the higher will be the ether content in the borate salt. To achieve an ether content in the borate salt of less than about 0.5 weight %, the head temperature during the distillation should not be less than about 109xc2x0 C. Surprisingly, when treated similarly, tetrakis(pentafluorophenyl) borate magnesium bromide is not rendered ether free. To isolate sodium or potassium tetrakis(pentafluorophenyl) borate, ether may be distilled from the other components. Upon cooling, the borate salt will precipitate out of solution and may be removed by filtration. Alternatively, toluene may be removed by distillation at atmospheric pressure or, preferably, under vacuum, to provide the borate salt.
In accordance with a further preferred embodiment, the present invention relates to the manufacture of trityl tetrakis(pentafluorophenyl) borate. A slurry of substantially ether-free tetrakis(pentafluorophenyl) sodium borate is reacted with trityl chloride in a hydrocarbon of six to ten carbons, preferably a non-aromatic hydrocarbon, more preferably heptane, to form a slurry of trityl tetrakis(pentafluorophenyl) borate and sodium chloride in heptane. The reaction occurs slowly at room temperature, but is more efficiently accomplished at reflux (about 98xc2x0 C.) for a period of from about 0.5 to about 10 hours, and more preferably from about 1 to about 3 hours. The amount of trityl chloride used should be at least one mole of trityl chloride per mole of sodium salt, but a slight excess is preferred (from about 1.05 to about 3 equivalents and more preferably from about 1.1 to about 1.6 equivalents). The solid products are removed from the heptane by a suitable method, such as filtration or decantation. Trityl tetrakis(pentafluorophenyl) borate is then selectively dissolved in a halogenated solvent that does not contain oxygen, nitrogen, or other coordinating atoms. Appropriate solvents are selected from the halogenated solvents selected from the group consisting of methylene chloride(CH2Cl2), chloroform (CHCl3), carbon tetrachloride (CCl4) and trichlorotrifluoroethane (CF3CCl3). The trityl tetrakis(pentafluorophenyl) borate solution is then diluted with a hydrocarbon solvent having a higher boiling point than the halogenated solvent, such as heptane, followed by distillation to remove all organic solvents to provide essentially ether-free, yellow, trityl tetrakis(pentafluorophenyl) borate. It is understood, that the term xe2x80x9cessentially ether-freexe2x80x9d refers to an ether content in the final trityl tetrakis(pentafluorophenyl) borate of less than about 0.5 weight percent, preferably less than about 0.3 weight percent, and more preferably less than about 0.1 weight percent. Therefore the process of the present invention produces, for the first time, a solid, ether-free trityl tetrakis(pentafluorophenyl) borate that is yellow in color (as opposed to the known orange color).
Surprisingly, the sodium borate salt used in the preparation of the trityl borate salt may contain small amounts of ether and/or water, which will not be transferred to the trityl salt using the preferred embodiments of this invention. The ether content of the sodium salt should not exceed about 3.0 weight percent, is preferably about less than about 1.0 weight percent, and still more preferably it should not exceed about 0.5 weight percent. The limits on amount of water present are similar. Exceeding the preferred limits may not prevent the formation of the trityl borate salt, but if exceeded, water and ether may be present in the final trityl borate product. It is understood that the presence of water will then require a separate step to remove it. Drying over molecular sieves has been ineffective, but chemical drying can be used.
As stated above, known prior methods for manufacture of the desired product result in foaming or blooming, which is disadvantageous. According to the present invention, to isolate solid product without xe2x80x9cbloomingxe2x80x9d, a hydrocarbon solvent comprising a six to ten carbon hydrocarbon compound is added to the halogenated solvent to create a solvent mixture. The solvent is then distilled off to give a slurry of the borate in the hydrocarbon solvent which is then filtered. Therefore, the process of the present invention not only produces an ether-free form of the desired trityl tetrakis(pentafluorophenyl) borate, but the borate is produced for the first time as a yellow product, and is synthesized in an efficient manner in high purity without wasteful xe2x80x9cbloomingxe2x80x9d or foaming.